The DC dirge “Joker: Folie à Deux” is a sequel in search of a purpose. For nearly two and a half hours, director Todd Phillips’ pathologically unnecessary movie cycles through so many potential reasons to exist. But, as “Deux” grows increasingly disturbing, repulsive and strange on the hunt, it ultimately never finds a satisfying one.

First, the film exhaustingly tries dragging out the story of Arthur Fleck, the mentally ill aspiring standup who snapped and killed a late-night talk show host on live TV in the last one . Joaquin Phoenix won an Oscar for playing the traumatized loser who is essentially Robert De Niro in “The King of Comedy,” plus clown makeup. So, let’s milk it for all it’s worth.

But the truth is that the whack-job Gothamite with no Batman to battle is more weird than he is involving. Aimless, Arthur whispers, glares, yells, rails against the world and does his creepy laugh again and again with nothing to show for it. This time, we care neither for nor about him.

Since Arthur’s static journey behind bars alone is not meaty enough for a second chapter, another justification “Deux” flirts with is a creepy concert for Phoenix and Lady Gaga. The pop-star-turned-actress plays Harleen “Lee” Quinzel — aka Harley Quinn — a troubled woman locked up in Arkham Prison enamored with Arthur and his rage-driven Joker persona. He’s become a cult hero since his six-victim killing spree, and a made-for-TV movie about his crimes has gained him.